A duct formed by connecting a first pipe and a second pipe to both sides of an extensible flexible pipe joint is embedded in the ground, and a fluid is transferred, for example, waste water is discharged and so on.
With the passage of time, positions of the first pipe and the second pipe with respect to the extensible flexible pipe joint may be possibly slipped (displaced) from the original embedded positions, because the duct in the ground is subjected to an earthquake influence or the like. Because of this unavoidable positional slippages of the first pipe and the second pipe with respect to the extensible flexible pipe joint, the first pipe and/or the second pipe may be detached from the extensible flexible pipe joint so that they do not constitute a normal duct.
Thus, the first pipe and the second pipe are preferably maintained/repaired or replaced, before the positional slippage of the first pipe or the second pipe becomes excessively serious.
To this end, it is necessary to monitor the positional relationships of the first pipe and the second pipe with respect to the extensible flexible pipe joint occasionally or periodically.
Conventionally, in order to monitor the positional relationships of the first pipe and the second pipe with respect to the extensible flexible pipe joint, the embedded extensible flexible pipe joint is exposed as a whole by digging up the ground, and the positional relationships of the first pipe and the second pipe with respect to the extensible flexible pipe joint is inspected.
Instead of digging up the ground to expose the embedded extensible flexible pipe joint for inspection, the following method is proposed. Namely, a plurality of wires inserted through tubes are used. Respective ends of the wires are connected at intervals around the extensible flexible pipe joint, and the other ends are drawn up to the ground. By mechanically measuring a displacement of the wire with respect to the tube, the positional relationships among the extensible flexible pipe joint and so on are inspected.
However, when the plurality of wires are used, this method is unreliable because there are some problems in that the tubes in the ground are deteriorated, relative movement between the wire and the tube cannot be smoothly conducted because of sands or dusts which enter a space between the wire and the tube, and so on. In addition, since information about slippage data of the relative positional relationship between the wire and the tube is mechanically detected as a mechanical displacement amount of the wire itself, the method is unreliable and efficient measurement cannot be achieved.
Patent Document 1: JP03-285137A
Patent Document 2: JP2005-091215A
Patent Document 3: JP2004-053317A
Patent Document 4: JP2004-010355A